Typical double hung windows have at least one vertically sliding window sash with pivots at the bottom corners of the window sash and releasable latches near the top corners of the sash that disengage from tracks in the window frame to allow the window to tilt in for ease of cleaning. These releasable latches are most commonly actuated by means of rotating or sliding levers (commonly known as tilt latches) positioned on the top surface of the sash, which operate to retract the locking points from tracks in the window jamb. The most typical embodiment of this latching arrangement involves a separate lever or similar operator designed to engage and disengage each latch, resulting in multiple operating mechanisms protruding from the window sash and the need to actuate multiple operators in order to tilt in the window.
An established shortcoming of the typical tilt-in style double hung window is that sometimes there is a lack of an adequate seal between the window sash and the jamb of the window frame. In order for the double hung window to tilt in freely upon disengagement of the releasable latches, the portion of the window sash between the pivot points at its base and the releasable latches at the upper end cannot be permanently fastened within the window frame. As a result, high perpendicular forces against the window, resulting from strong winds, for example, can result in inward bowing of the window sash and distortion of the sash and frame sealing edges. This problem is even more pronounced with larger windows having larger gaps between pivot and upper latch points, or windows in multi-story office or apartment buildings, which are routinely exposed to high velocity winds at the upper floors.
To overcome this problem, additional locking mechanisms can be added to the sides of the window sash at an intermediate point between the pivot points and the releasable latches. U.S. Pat. No. 4,525,952 to Cunningham et al. discloses a tilt-in window with two levers at the top of the window sash designed to retract two upper latches, and two levers on the sides of the window sash that retract two additional latches, intended to provide additional stability for the window and an improved seal. While this addresses some aspects of the inward bowing concerns, the multiple levers result in a cumbersome process for locking and unlocking the window sash, as well as an aesthetically cluttered window design.
The inconvenience of operating two release levers to retract upper latches to tilt in the window sash has prompted the development of window designs employing a single, centrally located handle or lever designed to retract both tilt latches, through use of such mechanisms as a linked cam or retracting cables. See, for example, U.S. Pat. No. 5,992,907 to Sheldon et al., U.S. Pat. No. 5,090,750 to Lindqvist, and U.S. patent application Ser. No. 10/041,784 to Marshik. However, the problem of effectively and conveniently retracting both traditional upper latches and intermediate (anti-bow) locking mechanisms has not been addressed. Further, by themselves, the simple mechanical means of retracting these locking latches, as disclosed in the prior art, are not capable of retracting additional locking points that are not horizontally in-line with the lever and upper locking points.